SpringBoot 源码分析(四) 内置Tomcat分析

一、Tomcat相关知识

1. tomcat目录结构

Tomcat文件的目录结构

2.启动流程

启动一个Tomcat服务是执行的bin目录下的脚本程序，startup.bat和 startup.sh.一个是windows的脚本，一个是Linux下的脚本，同样还可以看到两个停止的脚本 shutdown.bat 和 shutdown.sh.

startup.bat脚本内容

catalina.bat脚本文件
doStart方法

最后会执行的程序是


MAINCLASS变量是就是Bootstrap.class

3.Bootstrap类

3.1 架构图

Tomcat的架构图如下所示

3.2 流程分析

Bootstrap中的main方法是入口；

bootstrap.init(); // 初始化类加载器
bootstrap.load(); // 间接调用Catalina，创建对象树，然后调用生命周期的init方法初始化整个对象树
bootstrap.start(); // 间接调用Catalina的start方法，然后调用生命周期的start方法启动整个对象树

二、SpringBoot内嵌Tomcat原理

在使用springboot搭建一个web应用程序的时候，我们发现不需要自己搭建一个tomcat服务器，只需要引入spring-boot-starter-web,在应用启动时会自动启动嵌入式的tomcat作为服务器，而tomcat的实现机制也是从自动装配开始的。

1、ServletWebServerFactoryAutoConfiguration

@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
		ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
		ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
		ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {

	@Bean
	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(ServerProperties serverProperties) {
		return new ServletWebServerFactoryCustomizer(serverProperties);
	}

	@Bean
	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new TomcatServletWebServerFactoryCustomizer(serverProperties);
	}

	@Bean
	@ConditionalOnMissingFilterBean(ForwardedHeaderFilter.class)
	@ConditionalOnProperty(value = "server.forward-headers-strategy", havingValue = "framework")
	public FilterRegistrationBean<ForwardedHeaderFilter> forwardedHeaderFilter() {
		ForwardedHeaderFilter filter = new ForwardedHeaderFilter();
		FilterRegistrationBean<ForwardedHeaderFilter> registration = new FilterRegistrationBean<>(filter);
		registration.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.ASYNC, DispatcherType.ERROR);
		registration.setOrder(Ordered.HIGHEST_PRECEDENCE);
		return registration;
	}

	/**
	 * Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
	 * {@link ImportBeanDefinitionRegistrar} for early registration.
	 */
	public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {

		private ConfigurableListableBeanFactory beanFactory;

		@Override
		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
			if (beanFactory instanceof ConfigurableListableBeanFactory) {
				this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
			}
		}

		@Override
		public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
				BeanDefinitionRegistry registry) {
			if (this.beanFactory == null) {
				return;
			}
			registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
					WebServerFactoryCustomizerBeanPostProcessor.class);
			registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor",
					ErrorPageRegistrarBeanPostProcessor.class);
		}

		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
			if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
				beanDefinition.setSynthetic(true);
				registry.registerBeanDefinition(name, beanDefinition);
			}
		}
	}
}

从这个类上可以看到，当前配置类主要导入了BeanPostProcessorRegister,该类实现了ImportBeanDefinitionRegister接口，可以用来注册额外的BeanDefinition，同时，该类还导入了EmbeddedTomcat，EmbeddedJetty，EmbeddedUndertow三个类，可以根据用户的需求去选择使用哪一个web服务器，默认情况下使用的是tomcat

2、onRefresh()

当自动装配功能完成之后会接着执行onRefresh的方法（ServletWebServerApplicationContext）

@Override
protected void onRefresh() {
    //创建主题对象，不用在意
	super.onRefresh();
	try {
        //开始创建web服务
		createWebServer();
	}
	catch (Throwable ex) {
		throw new ApplicationContextException("Unable to start web server", ex);
	}
}

3、createWebServer()

创建web服务，默认获取的是tomcat的web容器（ServletWebServerApplicationContext）

private void createWebServer() {
	WebServer webServer = this.webServer;
	ServletContext servletContext = getServletContext();
	if (webServer == null && servletContext == null) {
        //获取servletWebServerFactory,从上下文注册bean中可以找到
		ServletWebServerFactory factory = getWebServerFactory();
        //获取servletContextInitializer,获取webServer
		this.webServer = factory.getWebServer(getSelfInitializer());
	}
	else if (servletContext != null) {
		try {
			getSelfInitializer().onStartup(servletContext);
		}
		catch (ServletException ex) {
			throw new ApplicationContextException("Cannot initialize servlet context", ex);
		}
	}
    //替换servlet相关的属性资源
	initPropertySources();
}

如何获取tomcat的bean的实例对象呢？从如下代码中可以看出

ServletWebServerApplicationContext

protected ServletWebServerFactory getWebServerFactory() {
		// Use bean names so that we don't consider the hierarchy
		String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
		if (beanNames.length == 0) {
			throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
					+ "ServletWebServerFactory bean.");
		}
		if (beanNames.length > 1) {
			throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
					+ "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
		}
		return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
	}

protected ServletWebServerFactory getWebServerFactory() {
		// Use bean names so that we don't consider the hierarchy
		String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
		if (beanNames.length == 0) {
			throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
					+ "ServletWebServerFactory bean.");
		}
		if (beanNames.length > 1) {
			throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
					+ "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
		}
		return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
	}

DefaultListableBeanFactoryf

/*
第一个参数type表示要查找的类型
第二个参数表示是否考虑非单例bean
第三个参数表示是否允许提早初始化
*/
@Override
	public String[] getBeanNamesForType(@Nullable Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
        //配置还未被冻结或者类型为null或者不允许早期初始化
		if (!isConfigurationFrozen() || type == null || !allowEagerInit) {
			return doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, allowEagerInit);
		}
        //此处注意isConfigurationFrozen为false的时候表示beanDefinition可能还会发生更改和添加，所以不能进行缓存，如果允许非单例bean，那么从保存所有bean的集合中获取，否则从单例bean中获取
		Map<Class<?>, String[]> cache =
				(includeNonSingletons ? this.allBeanNamesByType : this.singletonBeanNamesByType);
		String[] resolvedBeanNames = cache.get(type);
		if (resolvedBeanNames != null) {
			return resolvedBeanNames;
		}
        //如果缓存中没有获取到，那么只能重新获取，获取到之后就存入缓存
		resolvedBeanNames = doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, true);
		if (ClassUtils.isCacheSafe(type, getBeanClassLoader())) {
			cache.put(type, resolvedBeanNames);
		}
		return resolvedBeanNames;
	}

private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
		List<String> result = new ArrayList<>();

		// Check all bean definitions.
		for (String beanName : this.beanDefinitionNames) {
			// Only consider bean as eligible if the bean name
			// is not defined as alias for some other bean.
            //如果时别名则跳过（当前集合会保存所有的主beanname，并且不会保存别名，别名由beanfactory中别名map维护）
			if (!isAlias(beanName)) {
				try {
                    //获取合并的beandefinition，合并的beandefinition是指spring整合了父beandefinition的属性，将其beandefinition编程了rootBeanDefinition
					RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
					// Only check bean definition if it is complete.
                    //抽象的beandefinition是不做考虑，抽象的就是拿来继承的，如果允许早期初始化，那么直接短路，进入方法体，如果不允许早期初始化，那么需要进一步判断，如果是不允许早期初始化的，并且beanClass已经被加载或者它是可以早期初始化的，那么如果当前bean是工厂bean，并且指定的bean又是工厂那么这个bean就必须被早期初始化，也就是说就不符合我们制定的allowEagerInit为false的情况，直接跳过

					if (!mbd.isAbstract() && (allowEagerInit ||
							(mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading()) &&
									!requiresEagerInitForType(mbd.getFactoryBeanName()))) {
                        //如果当前bean是工厂bean
						boolean isFactoryBean = isFactoryBean(beanName, mbd);
                        //如果允许早期初始化，那么基本上会调用最后的isTypeMatch方法，这个方法会导致工厂的实例化，但是当前不允许进行早期实例化在不允许早期实例化的情况下，如果当前bean是工厂bean，那么它只能在已经被创建的情况下调用isTypeMatch进行匹配判断否则只能宣告匹配失败，返回false
						BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
						boolean matchFound = false;
						boolean allowFactoryBeanInit = allowEagerInit || containsSingleton(beanName);
						boolean isNonLazyDecorated = dbd != null && !mbd.isLazyInit();
						if (!isFactoryBean) {
							if (includeNonSingletons || isSingleton(beanName, mbd, dbd)) {
								matchFound = isTypeMatch(beanName, type, allowFactoryBeanInit);
							}
						}
						else  {
                            //如果没有匹配到并且他是个工厂bean，那么加上&前缀，表示要获取factorybean类型的bean
							if (includeNonSingletons || isNonLazyDecorated ||
									(allowFactoryBeanInit && isSingleton(beanName, mbd, dbd))) {
								matchFound = isTypeMatch(beanName, type, allowFactoryBeanInit);
							}
							if (!matchFound) {
								// In case of FactoryBean, try to match FactoryBean instance itself next.
								beanName = FACTORY_BEAN_PREFIX + beanName;
								matchFound = isTypeMatch(beanName, type, allowFactoryBeanInit);
							}
						}
                        //找到便记录到result集合中，等待返回
						if (matchFound) {
							result.add(beanName);
						}
					}
				}
				catch (CannotLoadBeanClassException | BeanDefinitionStoreException ex) {
					if (allowEagerInit) {
						throw ex;
					}
					// Probably a placeholder: let's ignore it for type matching purposes.
					LogMessage message = (ex instanceof CannotLoadBeanClassException) ?
							LogMessage.format("Ignoring bean class loading failure for bean '%s'", beanName) :
							LogMessage.format("Ignoring unresolvable metadata in bean definition '%s'", beanName);
					logger.trace(message, ex);
					onSuppressedException(ex);
				}
			}
		}
// Check manually registered singletons too.
    //从单例注册集合中获取，这个单例集合石保存spring内部注入的单例对象，他们的特点就是没有beanDefinition
		for (String beanName : this.manualSingletonNames) {
			try {
				// In case of FactoryBean, match object created by FactoryBean.
                //如果是工厂bean,那么调用其getObjectType去匹配是否符合指定类型
				if (isFactoryBean(beanName)) {
					if ((includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type)) {
						result.add(beanName);
						// Match found for this bean: do not match FactoryBean itself anymore.
						continue;
					}
					// In case of FactoryBean, try to match FactoryBean itself next.
					beanName = FACTORY_BEAN_PREFIX + beanName;
				}
				// Match raw bean instance (might be raw FactoryBean).
                //如果没有匹配成功，那么匹配工厂类
				if (isTypeMatch(beanName, type)) {
					result.add(beanName);
				}
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Shouldn't happen - probably a result of circular reference resolution...
				logger.trace(LogMessage.format("Failed to check manually registered singleton with name '%s'", beanName), ex);
			}
		}

		return StringUtils.toStringArray(result);
	}

4、tomcat对象的初始化（ServletWebServerApplicationContext）

private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
		return this::selfInitialize;
	}

private void selfInitialize(ServletContext servletContext) throws ServletException {
    //使用给定的完全加载的servletContext准备WebApplicationContext
	prepareWebApplicationContext(servletContext);
	registerApplicationScope(servletContext);
    //使用给定的BeanFactory注册特定于web的作用域bean（contextParameters,contextAttributes）
	WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
	for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
		beans.onStartup(servletContext);
	}
}

5、完成内嵌tomcat的api调用（TomcatServletWebServerFactory）

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
	if (this.disableMBeanRegistry) {
		Registry.disableRegistry();
	}
    //完成tomcat的api调用
	Tomcat tomcat = new Tomcat();
	File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
	tomcat.setBaseDir(baseDir.getAbsolutePath());
	//创建连接器
	Connector connector = new Connector(this.protocol);
	connector.setThrowOnFailure(true);
	//Service相关连接器
	tomcat.getService().addConnector(connector);
	customizeConnector(connector);
	tomcat.setConnector(connector);
	//host相关
	tomcat.getHost().setAutoDeploy(false);
	configureEngine(tomcat.getEngine());
	for (Connector additionalConnector : this.additionalTomcatConnectors) {
		tomcat.getService().addConnector(additionalConnector);
	}
    //准备tomcatEmbeddedContext并设置到tomcat中
	prepareContext(tomcat.getHost(), initializers);
    //构建tomcatWebServer
	return getTomcatWebServer(tomcat);
}

6、getTomcatWebServer()

获取tomcat服务（TomcatServletWebServerFactory）

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
	return new TomcatWebServer(tomcat, getPort() >= 0);
}
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
	Assert.notNull(tomcat, "Tomcat Server must not be null");
	this.tomcat = tomcat;
	this.autoStart = autoStart;
    //初始化
	initialize();
}

7、initialize()

完成tomcat的初始化，其中this.tomcat.start();就是会进入到tomcat的逻辑了 这个需要单独看Tomcat的源码了。

private void initialize() throws WebServerException {
		logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
		synchronized (this.monitor) {
			try {
                //engineName拼接instanceId
				addInstanceIdToEngineName();

				Context context = findContext();
				context.addLifecycleListener((event) -> {
					if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
						// Remove service connectors so that protocol binding doesn't
						// happen when the service is started.
                        //删除Connectors，以便再启动服务时不发生协议绑定
						removeServiceConnectors();
					}
				});

				// Start the server to trigger initialization listeners
                //启动服务触发初始化监听器
				this.tomcat.start();

				// We can re-throw failure exception directly in the main thread
                //在主线程中重新抛出失败异常
				rethrowDeferredStartupExceptions();

				try {
					ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
				}
				catch (NamingException ex) {
					// Naming is not enabled. Continue
				}

				// Unlike Jetty, all Tomcat threads are daemon threads. We create a
				// blocking non-daemon to stop immediate shutdown
                //所有的tomcat线程都是守护线程，我们创建一个阻塞非守护线程来避免立即关闭
				startDaemonAwaitThread();
			}
			catch (Exception ex) {
                //异常停止tomcat
				stopSilently();
				destroySilently();
				throw new WebServerException("Unable to start embedded Tomcat", ex);
			}
		}
	}
-----------------------
    	private void removeServiceConnectors() {
		for (Service service : this.tomcat.getServer().findServices()) {
			Connector[] connectors = service.findConnectors().clone();
            //将将要移除的conntector放到缓存中暂存
			this.serviceConnectors.put(service, connectors);
			for (Connector connector : connectors) {
                //移除connector
				service.removeConnector(connector);
			}
		}
	}

start方法

8、finishRefresh()中tomcat的处理

除了refresh方法之外，在finishRefresh()方法中也对tomcat做了相关的处理（ServletWebServerApplicationContext）

	protected void finishRefresh() {
        //调用父类的finishRefresh方法
		super.finishRefresh();
        //启动webServer
		WebServer webServer = startWebServer();
		if (webServer != null) {
            //发布webServer初始化完成事件
			publishEvent(new ServletWebServerInitializedEvent(webServer, this));
		}
	}

ServletWebServerApplicationContext

	private WebServer startWebServer() {
		WebServer webServer = this.webServer;
		if (webServer != null) {
            //启动webserver
			webServer.start();
		}
		return webServer;
	}

TomcatWebServer

	public void start() throws WebServerException {
		synchronized (this.monitor) {
			if (this.started) {
				return;
			}
			try {
                //添加之前移除的connector
				addPreviouslyRemovedConnectors();
				Connector connector = this.tomcat.getConnector();
				if (connector != null && this.autoStart) {
                    //延迟加载启动
					performDeferredLoadOnStartup();
				}
                //检查connector启动状态是否为失败，失败抛出异常
				checkThatConnectorsHaveStarted();
				this.started = true;
				logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"
						+ getContextPath() + "'");
			}
			catch (ConnectorStartFailedException ex) {
                //异常停止tomcat
				stopSilently();
				throw ex;
			}
			catch (Exception ex) {
				if (findBindException(ex) != null) {
					throw new PortInUseException(this.tomcat.getConnector().getPort());
				}
				throw new WebServerException("Unable to start embedded Tomcat server", ex);
			}
			finally {
				Context context = findContext();
                //context解绑classload
				ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
			}
		}
	}

private void addPreviouslyRemovedConnectors() {
		Service[] services = this.tomcat.getServer().findServices();
		for (Service service : services) {
            //从上面移除connector添加的缓存中取出connector
			Connector[] connectors = this.serviceConnectors.get(service);
			if (connectors != null) {
				for (Connector connector : connectors) {
                    //添加到tomcat service中
					service.addConnector(connector);
					if (!this.autoStart) {
                        //如果不是自动启动，则暂停connector
						stopProtocolHandler(connector);
					}
				}
                //添加完成后移除
				this.serviceConnectors.remove(service);
			}
		}
	}

private void performDeferredLoadOnStartup() {
		try {
			for (Container child : this.tomcat.getHost().findChildren()) {
				if (child instanceof TomcatEmbeddedContext) {
                    //延迟加载启动
					((TomcatEmbeddedContext) child).deferredLoadOnStartup();
				}
			}
		}
		catch (Exception ex) {
			if (ex instanceof WebServerException) {
				throw (WebServerException) ex;
			}
			throw new WebServerException("Unable to start embedded Tomcat connectors", ex);
		}
	}

	void deferredLoadOnStartup() throws LifecycleException {
		doWithThreadContextClassLoader(getLoader().getClassLoader(),
				() -> getLoadOnStartupWrappers(findChildren()).forEach(this::load));
	}

9、应用上下文关闭时会调用tomcat的关闭

在refreshContext中注册一个关闭的钩子函数，而钩子函数可以完成关闭的功能

ServletWebServerApplicationContext

	@Override
	protected void onClose() {
		super.onClose();
		stopAndReleaseWebServer();
	}

	private void stopAndReleaseWebServer() {
		WebServer webServer = this.webServer;
		if (webServer != null) {
			try {
				webServer.stop();
				this.webServer = null;
			}
			catch (Exception ex) {
				throw new IllegalStateException(ex);
			}
		}
	}

TomcatWebServer

@Override
	public void stop() throws WebServerException {
		synchronized (this.monitor) {
			boolean wasStarted = this.started;
			try {
				this.started = false;
				try {
					stopTomcat();
					this.tomcat.destroy();
				}
				catch (LifecycleException ex) {
					// swallow and continue
				}
			}
			catch (Exception ex) {
				throw new WebServerException("Unable to stop embedded Tomcat", ex);
			}
			finally {
				if (wasStarted) {
					containerCounter.decrementAndGet();
				}
			}
		}
	}